Rate-selectable multimode trellis-coded 8PSK system

A multimode method for trellis-coded modulation (TCM) is proposed to construct various rate TCM schemes. The multimode trellis-coded (TC) 8PSK schemes with rates of 1/2, 4/9, 5/9, 5/12, and 7/12 are demonstrated. These are obtained from the combination of conventional single-mode TC-8PSK with rates 1/3 and 2/3. By investigating the trellis structure and code search, a new multimode trellis diagram is found, which provides a better Euclidean distance property than that by merely combining optimum single-mode trellis diagrams. As for bit error rate (BER) performances, the BER expression is derived and estimated for multimode TCM schemes.